Method of cooling a packaged electronic device

ABSTRACT

A removable heatsink assembly comprised of a heatsink unit and a heatspreader is provided. The heatsink unit has at least one fin and a coupling collar for radiating heat away from a packaged electronic device. The heatspreader includes a platform attached to an inner collar in thermal contact with the packaged electronic device. The platform has one or more tabs suitable for mating with one or more flanges located on the coupling collar of the heatsink unit. Coupling grooves within the flanges engage the platform of the heatspreader when the flanges are mated with the heatspreader tabs and the heatsink is turned. The heatsink can therefore be quickly and conveniently attached to or removed from the heatspreader. The present invention thus permits a wide variety of different heatsinks to be interchangeably used with a single heatspreader attached to an electronic device package.

CROSS REFERENCE TO RELATED APPLICATION

This is a continuation of application Ser. No. 08/317,968, filed Oct. 4,1994, which issued on Oct. 31, 1995 as U.S. Pat. No. 5,463,529 which isa continuation of Ser. No. 08/023,981, filed Feb. 6, 1993, which issuedas U.S. Pat. No. 5,353,193.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a heatsink for dissipating heat fromintegrated circuits or other electronic devices and, more particularly,relates to a removable heatsink capable for providing varying amounts ofpower dissipation.

2. Description of Related Art

Heatsinks are important components in integrated circuits and otherelectronic packaged devices which consume power and generate heat. Theheatsink draws heat away from the electronic device it is attached toand dissipates the heat into the surrounding environment. Typically, theheatsink will be affixed to an electronic device at the package level.For example, in the case of an integrated circuit, the heatsink isusually attached when the integrated circuit is coated with plastic,metal, ceramic, or otherwise packaged. In the remaining discussion andthroughout this specification, integrated circuits will be referred toas exemplary electronic devices to which the present invention relates.However, it should be understood that the discussion also applies toother types of packaged electronic devices.

An integrated circuit should employ a heatsink capable of dissipatingthe heat that is generated when the integrated circuit is operating atmaximum power consumption. Such heatsinks, however, are larger than theymight otherwise be since a particular board application for anintegrated circuit might generate less heat than the same integratedcircuit would generate when operating at maximum power. Attaching aheatsink at the package level is therefore inflexible and inefficient inthat the size of the heatsink cannot be tailored to the needs of aparticular application. Furthermore, installing the heatsink prior toproduction of circuit boards or other devices which incorporateintegrated circuits may needlessly increase the cost of the devices aswell as make them more difficult to handle and process. Permanentheatsink attachment methods using glue or epoxy require additionalcuring steps and cannot be readily removed after attachment.

The above problems with conventional heatsinks have created a need forremovable heatsinks so that different sized heatsinks can be quickly andconveniently applied to integrated circuits as appropriate to aparticular application. Various removable heatsinks exist in the priorart. U.S. Pat. No. 4,716,494, issued to Bright et al., discloses aretention system for a removable heatsink using a spring clip. However,the clip is cumbersome, adds additional weight to the integratedcircuit, and requires special adoptive retention projections which mustbe carefully aligned on the integrated circuit. The clip also haspractical drawbacks of taking up unnecessary space and potentiallyleading to damage of the integrated circuit due to excessive forceexerted by the spring.

U.S. Pat. No. 4,729,426, issued to Hinshaw, discloses a bonded clipheatsink incorporating a clip of resilient material which is bonded tothe heatsink body and adopted to grip the electronic device packaged tosecure the electronic device. The clip is cumbersome, takes upunnecessary space and is not truly removable.

U.S. Pat. No. 4,978,638, issued to Buller et al., discloses a method forattaching a heatsink to a plastic package integrated circuit. However,Buller requires the additional step of gluing the heatsink or its mountonto the package. The method disclosed therein is not readily adaptableto other types of electronic device packages, since the mounting meansmust have a certain amount of resiliency in order for the heatsink to besnapped into place. In addition, the contact between the heat sink andthe package is not maintained through the application of downward force,but instead the heatsink is held in place via lateral force.

U.S. Pat. No. 4,712,159, issued to Clemens, discloses a heatsink clipassembly which requires an additional clip and end locking prongs. Thisassembly is cumbersome, requires unnecessary additional parts and is noteasily removable. Furthermore, a non-removable prong platform disposedbeneath the integrated circuit is required. All of the above describedpatents have attendant disadvantages in that they either are not easilyremovable or require clipping methods which add bulk and unnecessaryweight and are therefore not convenient to use within the very tighttolerances of a modern printed circuit board.

As is apparent from the above, there presently is a need for a removableheatsink and heatspreader assembly in which the heatsink can be easilyand conveniently removed from the heatspreader. The removable heatsinkshould permit matching of a desired size and type of heatsink to theperformance characteristics of an integrated circuit used in aparticular application. The removable heatsink should be easilyremovable and yet require no additional clips or other parts.Furthermore, the removable heatsink should not violate circuit boardtolerance restrictions by taking up additional space on the board, yetshould be readily adaptable for use with a wide variety of electronicdevice packages.

SUMMARY OF THE INVENTION

The present invention provides a removable heatsink which overcomes theabove identified problems in the prior art. The heatsink assembly of thepresent invention is comprised of a heatsink and a heatspreader. Theheatsink is comprised of at least one fin portion for radiating heataway from a packaged electronic device and a radiation portion to whichthe fin portion is attached. The radiation portion includes a couplingportion which has a collar. The heatspreader is in thermal contact withan electronic device package and comprises a platform portion and tabportions. The collar portion of the heatsink is designed so as to matewith the tab portions of the heatspreader. When the collar portion ofthe heatsink is aligned with the tab portions of the heatspreader, theheatsink is turned and the collar of the heatsink engages theheatspreader.

In accordance with one aspect of the present invention, the heatspreaderincludes spring loaded balls which exert a downward force on the collarportion of the heatsink when the heatsink is engaged to theheatspreader. In this manner, a strong thermal contact is maintainedbetween the heatspreader and the heatsink as long as the two areengaged. Heat is therefore efficiently transferred from the electronicdevice package through the heatspreader into the heatsink where it canbe effectively dissipated.

As a feature of the present invention, the heatsink is easily removablefrom the heatspreader and electronic device package. The heatsink thusprovides the capability of selecting the optimal size and style ofheatsink for a particular application. The additional assembly steps andinflexibility associated with permanently attached heatsinks is therebyavoided. In addition, the present invention eliminates the additionalparts and cumbersome removal associated with the currently availableremovable heatsinks.

As another feature of the present invention, the heatsink extends onlyin an upward direction from the electronic device package, and does notinclude any elements which extend around the sides of the device. Theheatsink of the present invention thus does not create any toleranceproblems when used with devices which are assembled onto a denselypacked circuit board. The danger of inadvertent and potentially damagingcontact of the heatsink with the device leads during installation isalso greatly reduced.

As an additional feature of the present invention, the heatsink providesa strong thermal contact with the underlying electronic device packagewithout exerting force on the package itself, and without sacrificingease in removal. By incorporating the force generating elements whichhold the heatsink in contact with the heatspreader into the heatspreaderitself, a suitable force is maintained without exerting undue stress onthe package.

As a further feature of the present invention, the heatspreader may beincorporated into a wide variety of electronic device packagesregardless of package size, shape or construction material. Since anytype of heatsink can be easily attached to the component package usingthe heatspreader, the present invention can provide a standard forheatsink mounting hardware that will permit a high degree ofinterchangeability and design flexibility in electronic devicemanufacture. Instead of designing a device around a particular heatsink,electronic package designers can incorporate the heatspreader of thepresent invention knowing that users will have the flexibility to choosethe proper heatsink during production. Electronic devices will thereforebe more readily interchanged from one application to another, andduplicated heatsink design efforts with be significantly reduced.

The above-discussed features and attendant advantages of the presentinvention will become better understood by reference to the followingdetailed description of the preferred embodiments and the accompanyingdrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional exploded view of an exemplary heatsink and aheatspreader which comprise the heatsink assembly of the presentinvention.

FIG. 2 is a perspective view illustrating the removable engagement ofthe heatsink and heatspreader of FIG. 1.

FIG. 3 is an exploded view of an alternative embodiment of the presentinvention.

FIG. 4 is a perspective view of an alternative embodiment of the presentinvention incorporating a square fin heatsink.

FIG. 5 is a side elevation illustrating how the heatsink andheatspreader of FIGS. 1 and 2 are removably coupled together.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention provides a removable heatsink which can be quicklyand easily detached from a heatspreader attached to an electronic devicepackage. The following detailed description describes exemplaryembodiments of the present invention as applied to integrated circuitpackages. It should be understood, however, that the present inventionmay also be applied to any other electronic package which dissipatespower and thereby generates heat. Furthermore, an almost unlimitedvariety of heatsinks may be used in accordance with the presentinvention. The exact size and shape of the heatsink can be tailored tofit the needs of a particular application without deviating from theprinciples of the present invention.

The exemplary embodiment of FIG. 1 illustrates the basic operation ofthe present invention as applied to an exemplary integrated circuitpackage. The heatsink assembly is comprised of a heatsink unit 10 and aheatspreader 9. The heatspreader 9 is in thermal contact with anelectronic device package 11 having a plurality of external leads 12. Inthe case of an integrated circuit, the leads 12 are part of a lead framecontained within the package 11. The heatspreader 9 is typicallycomprised of copper. The superior heat dissipation properties of thatmetal effectively draw the heat out of the integrated circuit package11. Alternatively, other heat conductive materials could also be-used.The package 11 can be of plastic, ceramic or other material commonlyused in the art. The removable heatsink unit 10 has a plurality ofradiating fins 3 and a coupling collar 4. The upper portions of theheatsink unit 10 is usually constructed of aluminum in order to conserveweight, but other conductive materials may also be suitable. Fins 3 aretypically comprised of an aluminum and not copper, in view of thelightness of aluminum and also in view of the fact that a larger surfacearea permits additional space for dissipation of heat. The couplingcollar 4 and flanges 5 should be constructed of a material such ascopper with good heat conduction properties in order to facilitate thetransfer of heat from the heatspreader 9 to the heatsink unit 10.

Coupling collar 4 includes flanges 5 having ramp-like inner couplinggrooves 6. The flanges 5 are adapted to be secured to ramp-likegenerally circumferential tabs 7 which are disposed generally underplatform 8 of heatspreader 9. The tabs are spaced a predetermineddistance above the upper surface 13 of package 11. The tabs 7 areadjacent the periphery of the platform 8 of heatspreader 9. In thepresent embodiment, inner collar portion 14 extends into the package 11and is attached to a lead frame within the integrated circuit package bymeans of a nonconductive glue or tape, as will be appreciated by thoseknowledgeable in integrated circuit packaging.

The heatsink unit 10 and heatspreader 9 are shown in engagement in FIG.2. Inner, coupling grooves 6 are adapted to slidably engage collarplatform 8 of heatspreader 9 via tabs 7. Ramp-like coupling grooves 6are tapered to engage tabs 7 such that heatsink unit 10 can be removablycoupled to platform 8 of heatspreader 9 by disposing coupling collar 4onto collar platform 8 and turning heatsink unit 10 onto collar platform8 and thereby into frictional engagement therewith. Ramp-like couplinggrooves 6 tighten about platform 8 as the heatsink unit 10 is turned.More specifically, as illustrated in FIG. 5, the lower surfaces of thetabs 7 are formed with ramps 15 which engage with ramps 16 formed on theupper surfaces of the flanges 5.

An exploded perspective view of a preferred embodiment of the presentinvention is shown in FIG. 3. The details of the integrated circuitpackage and heatsink assembly are as described in connection with FIGS.1 and 2 above. The heatsink unit 10 is illustrated as being operativelymounted on a printed circuit board 40. By reference to FIG. 3 the mannerin which flanges 5 and grooves 6 fit into tabs 7 and thereby engageplatform 8 is readily apparent.

As was previously mentioned, heatsink unit 10 is not limited tohorizontal circular radiating fins 3 as shown in FIGS. 1, 2 and 3 butcould instead include a wide variety of other heatsink sizes and shapes,depending upon the requirements of a particular application. Anexemplary alternative heatsink unit 30 is shown in FIG. 4. Heatsink unit30 includes a plurality of square vertically placed fins 31. It shouldbe noted that the heatspreader 9 is unchanged from the previousembodiment. Heatsink unit 30 will include a coupling collar, flanges andgrooves similar to those discussed above in order to engage platform 8of heatspreader 9 via tabs 7. This is illustrative of theinterchangeability of heatsink capability which is provided by thepresent invention. The concepts of the present invention thus includeall types of radiating surface areas that can be employed embodying theabove described concepts of the present invention.

The above described particular embodiments of the present inventionallow the heatspreader 9 and integrated circuit package 11 to beassembled at the packaging stage of operations and the heatsink unit 10thus need not be assembled onto heatspreader 9 until after theintegrated circuit has been packaged and the precise operatingenvironment for the integrated circuit or other electronic device hasbeen determined. If a particular integrated circuit application demandsonly a portion of the maximum power consumption of the integratedcircuit a smaller heatsink could be used than that required when thesame integrated circuit performs-at maximum power levels. For example,an integrated circuit operating at lower power levels might include onlya single fin. The exact heatsink surface area required will depend uponthe amount of power dissipated within the device to which it isattached.

The above invention thus provides a removable heatsink which need not beattached at the packaging stage and yet requires no additionalcumbersome clips or other fastening devices to attach the heatsink unitto the heatspreader. The proper heatsink can be precisely tailored tofit the intended use of a particular integrated circuit or otherelectronic device and therefore prevents the unnecessary waste ofadditional aluminum or other metal which might otherwise be part of aheatsink designed to accommodate maximum power dissipation requirementsfor a particular device. This contributes to efficient layout andmanufacture of circuit boards.

It will be understood by those skilled in the art that the abovedescription is by way of example only and that many alternateimplementations of this method are possible without deviating from thescope of the invention, which is limited only by the appended claims.For example, although not specifically illustrated, the ramps 15 on thetabs 7 can be replaced by spring loaded balls or other means forexerting a downward force on the flanges 5 of the heatsink 10 andmaintaining the heatsink 10 firmly attached to the heatspreader 9.

What is claimed is:
 1. A method of cooling a packaged electronic device,comprising the steps of:(a) providing the packaged electronic device;(b) providing a heatsink assembly, including:a removable heatsink unithaving at least one fin and a coupling collar; and a heatspreader havinga platform, at least one tab and an inner collar, said platform beingattached to said inner collar and said tab being disposed along theperiphery of said platform; (c) mounting said heatspreader on thepackaged electronic device such that said heatspreader is in thermalcontact with the packaged electronic device; and (d) removably couplingsaid heatsink unit to said heatspreader such that said heatspreaderreceives a portion of said coupling collar of said heatsink unit withinsaid tab, and when said heatsink unit is turned, said coupling collarremovably engages said platform of said heatspreader; whereby saidheatsink assembly radiates heat away from the packaged electronicdevice, and the packaged electronic device is thereby cooled.
 2. Themethod of claim 1 wherein step (a) comprises providing the packagedelectronic device as being comprised of a plastic material.
 3. Themethod of claim 1 wherein step (c) comprises mounting said heatspreaderon the packaged electronic device such that a portion of saidheatspreader is disposed within the packaged electronic device.
 4. Themethod of claim 1 wherein step (b) comprises providing said heatsinkassembly such that said coupling collar of said heatsink unit iscomprised of copper.
 5. The method of claim 1 wherein step (b) comprisesproviding said heatsink assembly such that said inner collar of saidheatspreader is comprised of copper.
 6. The method of claim 1 whereinstep (b) comprises providing said heatsink assembly such that said finof said heatsink unit is comprised of aluminum.
 7. The method of claim 1wherein step (b) comprises providing said heatsink assembly such thatsaid coupling collar of said heatsink unit and said platform of saidheatspreader are circular in shape.
 8. The method of claim 1 whereinstep (a) comprises providing the packaged electronic device as includingan integrated circuit.
 9. The method of claim 1, further comprising thesteps of:(e) providing a circuit board; and (f) mounting the packagedelectronic device on the circuit board.
 10. The method of claim 1wherein step (b) comprises providing said heatsink assembly such thatsaid portion of said coupling collar of said heatsink unit comprises aflange having an inner coupling groove.
 11. The method of claim 10wherein step (d) comprises engaging said flange with said tab such thatsaid inner coupling groove within said flange tightens about saidplatform as said heatsink unit is turned while said flange engages saidtab.
 12. The method of claim 10 wherein step (b) comprises providingsaid heatsink assembly such that said inner coupling groove has aramp-like surface.
 13. The method of claim 10 wherein step (b) comprisesproviding said heatsink assembly such that said coupling collar includestwo of said flanges, each of said flanges having an inner couplinggroove, and further wherein said heatspreader includes two tabs, each ofsaid tabs adapted for receiving one of said flanges.
 14. The method ofclaim 13 wherein step (b) comprises providing said heatsink assemblysuch that said two flanges are arranged on opposite sides of saidcoupling collar and said two tabs are arranged on opposite sides of saidplatform.
 15. A method of cooling a packaged electronic device,comprising the steps of:(a) providing the packaged electronic device;(b) providing a heatsink assembly for radiating heat away from thepackaged electronic device, including:a removable heatsink unit havingat least one fin and a coupling collar; a heatspreader having aplatform, at least one tab and an inner collar, said platform beingattached to said inner collar and said tab being disposed along theperiphery of said platform; (c) attaching said heatspreader to and inthermal contact with the packaged electronic device; (d) inserting aportion of said coupling collar of said heatsink unit within said tab;(e) turning said heatsink unit such that said coupling collar removablyengages said platform of said heatspreader, thereby removably couplingsaid heatsink unit to said heatspreader; and (f) exposing the packagedelectronic device and said heatsink assembly to an atmosphere into whichsaid heatsink assembly radiates heat away from the packaged electronicdevice, thereby cooling the packaged electronic device.
 16. The methodof claim 15, wherein step (a) comprises providing the packagedelectronic device as comprising a plastic material.
 17. The method ofclaim 15, wherein step (c) comprises disposing a portion of saidheatspreader within the packaged electronic device.
 18. The method ofclaim 15, wherein step (b) comprises providing said coupling collar ofsaid heatsink unit as comprising copper.
 19. The method of claim 15,wherein step (b) comprises providing said inner collar of saidheatspreader as comprising copper.
 20. The method of claim 15, whereinstep (b) comprises providing said fin of said heatsink unit ascomprising aluminum.
 21. The method of claim 15, wherein step (b)comprises providing said coupling collar of said heatsink unit and saidplatform of said heatspreader as being circular in shape.
 22. The methodof claim 15, wherein step (a) comprises providing the packagedelectronic device as comprising an integrated circuit.
 23. The method ofclaim 15, further comprising the step of:(f) mounting the packagedelectronic device on a circuit board.
 24. The method of claim 15,wherein step (b) comprises providing said portion of said couplingcollar of said heatsink unit as comprising a flange having an innercoupling groove.
 25. The method of claim 24, wherein step (e) comprisesturning said heatsink unit such that said flange engages said tab, andsaid inner coupling groove within said flange tightens about saidplatform while said flange engages said tab.
 26. The method of claim 24,wherein step (b) comprises providing said inner coupling groove ashaving a ramp-like surface.
 27. The method of claim 24, wherein step (b)comprises providing said coupling collar as including two of saidflanges, each of said flanges having an inner coupling groove, andfurther wherein said heatspreader includes two tabs, each of said tabsadapted for receiving one of said flanges.
 28. The method of claim 27,wherein step (b) comprises providing said two flanges as being arrangedon opposite sides of said coupling collar and said two tabs are arrangedon opposite sides of said platform.